Do you think it's possible the Democrats in Maryland will try to oust Harris anyway despite him winning? A bunch of things to consider:
1-There are plenty of Democrats on the Eastern Shore and in the state legislature.
2-Drawing the seat to be D+2 instead of R+13 isn't that hard.
3-Harris still has the Eastern Shore vs. Baltimore suburbs rivalry that won't go away.
4-Harris is not simply a mainstream conservative, he is an O'Donnell/Angle type. He was ranked by some article as the single most conservative member of the Maryland Senate, and frequently was on the losing side of votes where he was the only one voting against it (I suspect there will be similar votes in the House with him too, though they'll be more like 420-8 instead of one of course.)
If Harris is far-right, perhaps making his district more competitive could at least force him to be less extreme, even if he wouldn't lose. With MD-1 having a more Republican PVI than MD-2 or MD-3 is Democratic, would it be possible to make MD-1 more competitive without making Ruppersberger or Sarbanes at all vulnerable?